In many consumer packaging applications, it is important to prevent air or water from passing out of or into a package containing certain products. This is particularly true with respect to meat packages, cheese packages, and the like, for which the contained product must be kept in a constant environment to prevent spoilage. In order to preserve the product contained within such a package, the periphery of the package must be hermetically sealed. Hermetic seals can be provided by both permanent seals and temporary seals, known as peelable seals. Peelable seals are usable to provide a hermetic seal and, at the same time, provide a consumer with access to the contents of the package. A consumer breaks a peelable seal of a package by first grabbing onto opposing film faces to which peelable seal materials are adhered and then pulling the film faces apart.
A common method of packaging foods, such as sliced luncheon meats and the like, is by use of horizontal form, fill, and seal procedures. These procedures involve shaping a portion of film ("form"), placing the food article inside or upon the formed film portion ("fill"), completing the closure of the film portion around the food article and "sealing" open edges to complete the packaging process.
In some implementations, one sealing station is used to seal all the edges of a package and, at the same time, make a peelable seal from a strip of peelable materials. The sealing station has a set of seal bars, protruding from a sealing head, that press the package edges in the peelable strip against a resilient backing, such as rubber, to form both the permanent edge seals and the peelable seal. The strength of the seals is determined by the temperature, pressure, size of the seals, and dwell time of the seal bars.
Many packaging applications use resealable containers to store various types of articles and materials. These packages may be used to store and ship food products, non-food consumer goods, printed matter, correspondence, medical supplies, waste materials, and many other articles.
Resealable packages are convenient in that they can be closed and resealed after the initial opening to preserve the enclosed contents. The need to locate a storage container for the unused portion of the products in the package is thus avoided. As such, providing products in resealable packages appreciably enhances the marketability of those products.
The "sealing" stage of the form, fill, and seal procedure often involves using a resealable closure mechanism. The resealable closure mechanism and peelable seal are often produced as separate items fiom the package and are attached to and made integral with the package at a later point in the manufacturing process by a heat and pressure sealing process. Each separate closure profile includes a base strip and an interlocking member. In some conventional implementations, the closure profiles are formed by two separate extrusions or through two separate openings of a common extrusion die. One closure profile may have a rib or male member and the other, a mating groove or female member. The male or female member extends from the front face of the base strip. The rib and groove form a pressure-fastenable and releasable closure mechanism. The back side, or sometimes an extended portion of the front face of the base strip, is sealed to the package film so that the closure mechanism is disposed between the package walls adjacent to the openable side of the package. In some implementations, the packages are made of polymeric materials, since these materials inhibit the migration of air and water from and into the package. The packages can be either flexible or rigid.
To provide a peelable seal on a package with a resealable closure mechanism, the package typically uses permanent seals at its side edges and bottom edge and a peelable seal above or below the resealable closure mechanism at the mouth end of the package. In addition, the peelable seal may be arranged on either the flange/base portions of the closure mechanism or on the packaging film adjacent to the flange portions.
There are a couple of common implementations for forming peelable seals on resealable packages having a top and bottom film. One implementation adheres a multi-layered film to each of the opposing inner surfaces of the packaging film along the length of the mouth end of the package. This results in a first multi-layered film on the inner surface of the top film and a second multi-layered film on the inner surface of the bottom film. A peelable seal is formed by heat-sealing the first and second multi-layered films to one another. When a consumer breaks the peelable seal, one or more layers of the second multi-layered film will disengage from the other layers of the second multi-layered film and remain adhered to the first multi-layered film. As a result, the first multi-layered film will include at least one additional layer when the peelable seal is broken. The above layer disengagement upon breaking the peelable seal is accomplished by using film layers composed of different polymeric materials and by exploiting the varying bond strengths between the layers.
Another implementation adheres a layer of film to each of the opposing inner surfaces of the packaging film and introduces contaminants to one or both of the film layers. When the peelable seal is formed by heat-sealing the layers to one another, the bond between them is weak due to the surface contamination. Breaking the peelable seal detaches the layers from one another.
In order to preserve the product contained within a package, it is important that the peelable seal provides a hermetic seal. Peelable seals are highly susceptible to small variations that might occur during manufacture; ie., the peelable seals have low manufacturing tolerances. Given these manufacturing variations, it is possible for a peelable seal to not be hermetically sealed. In the current manufacturing process, it is difficult for the manufacturer to know which peelable seals are hermetically sealed and which are not. Furthermore, one purpose of the peelable seal is to provide a tamper resistant package to the consumer. With current peelable seals, it is difficult for the consumer to detect if the package has been tampered.